Cirrhosis of the liver is an increasingly common disease in the U.S, and hepatic stellate cells (HSC-i.e. lipocytes) are important effectors of liver fibrosis. Hepatocyte growth factor (HGF), a mitogen for hepatocytes and an inhibitor of liver fibrosis, is a secreted polypeptide whose gene expression is primarily restricted to stromal cells such as HSC. HGF acts in a paracrine fashion on epithelial cells (which do not express HGF) such as hepatocytes through its receptor Met. HSC lose HGF gene transcription rapidly as they transdifferentiate to myofibroblasts during liver fibrosis. The molecular basis of HGF gene regulation in HSC and liver fibrosis is not understood. Previously, we identified and characterized two 30-bp novel composite cis-acting elements in the HGF promoter which bind to several transcription factors such as PPARgamma, COUP-TF and C/EBPB It is well known that PPARgamma is a key regulator of adipocyte differentiation. PPARgamma and the other factors have not been studied in HSC differentiation and liver fibrosis; our preliminary data suggest that they modulate HGF gene expression in HSC during differentiation in vitro. We hypothesize that loss of HGF gene expression by HSC disrupts the HGF-mediated autocrine and/or paracrine circuits in the liver and is a determinant of liver fibrosis. In this renewal application, the PI proposes the following specific aims to continue this project: Aim 1: To test the hypothesis that HGF promoter composite elements (HPCE) functionally control HGF gene transcription in HSC in vivo. We will generate lines of transgenic mice harboring HGF promoter-EGFP reporter transgenes containing site-specific mutations in the HPCE. We will also develop mice in which the HPCE are mutated in the context of the endogenous HGF gene by gene targeting (i.e. HGF-promoter knock out mice) to investigate the implication of these promoter elements in HGF gene expression in HSC and liver fibrosis. Aim 2: To test the functionality of the transcription factors, particularly PPARgamma, which bind to HPCE in modulating endogenous HGF gene transcription in HSC and in maintaining hepatic stellate cell differentiation. We will determine the expression pattern and activities of these factors in HSC during the progression of liver fibrosis. We propose to overexpress PPARgamma in HSC in vitro as well as in vivo by generating transgenic mice that overexpress PPARgamma in HSC to investigate its effect on HGF gene transcription, HSC differentiation and liver fibrosis. Aim 3: To test the hypothesis that HGF-Met signaling is functionally important for maintenance of liver homeostasis including inhibition of liver fibrosis in adult animals. We will utilize mice that lack functional Met in the hepatocytes or HSC to dissect the mechanisms of how HGF mediates its anti-fibrotic effect in the liver.